Project Summary/Abstract Early childhood vaccinations are one of the most important public health interventions of the past century; however, vaccine coverage in the rural U.S. has lagged behind urban areas. Montana, a largely rural state, has suffered from persistently low vaccination rates and a resurgence of vaccine-preventable diseases among young children. There is currently a lack of evidence explaining Montana's low early childhood vaccination rates. Structural barriers may be a factor, including a high proportion of medically-underserved areas, transportation obstacles, and a lack of systems for reminding parents to return for additional vaccine doses. Our preliminary analyses suggest that parental vaccine hesitancy may also be on the rise in Montana, with an increasing number of parents choosing to delay or refuse vaccines for their children. To effectively target interventions to increase vaccination rates, there is a need to systematically distinguish how much of Montana's undervaccination problem is due to structural barriers versus parental vaccine hesitancy, and whether certain barriers are more common in certain areas of Montana. We will quantify the impact of structural barriers versus parental vaccine hesitancy barriers on Montana's low early childhood vaccination rates (Aim 1), identify factors associated with low vaccination rates in Montana, including whether specific barriers to vaccination are geographically clustered (Aim 2), and identify interventions to increase vaccination rates supported by the Montana medical community (Aim 3). These aims will be achieved through analysis of immunization records in Montana's centralized immunization information system for children ages 0-3 years who were born in Montana 2015-2017, and through a state-wide survey of pediatric and family medicine providers. The proposed work is fundamental to improving Montana's vaccine coverage because interventions to increase vaccine uptake differ based on the type of barrier being addressed. For example, structural barriers may be addressed by recruiting additional vaccine providers, implementing reminder/recall programs, or establishing vaccine clinics in non-traditional settings. In contrast, interventions to address vaccine hesitancy include motivational interviewing, parent education programs, and interactive social media tools. Based on our findings, we will pinpoint specific interventions to increase early childhood vaccine coverage in Montana, and we will submit a R01 application to the National Institutes of Allergy and Infectious Diseases to implement and test such interventions. This work is an important step toward eliminating national rural-urban disparities in early childhood vaccination rates.